2) Distance of the test material to the source
3) Diameter of the source
d) Instrument wavelengths
e) Instrument linearity
f) Sample being tested
g) Other factors as appropriate (e.g., polarization, spectral bandpass, scattered light, etc.).

2.2.8.4 The uncertainty should be computed according to NIST Technical Note 1297, Guidelines for
Evaluating and Expressing the Uncertainty of NIST Measurement Results.

2.2.8.5 The method used to fasten the calibration item on a fixture should be described in detail. In
general, differences in fastening between calibration and use will introduce errors in calibration.

2.3, Radiance temperature

2.3.1 Scope

This section contains specific technical criteria which a laboratory should meet if it is to be recognized as
competent to carry out radiance temperature calibrations.

2.3.2 References

a) Radiance Temperature Calibrations. C. E. Gibson, B. K. Tsia, and A.C. Parr, NIST Special Publication
250-43 (1998).

b) Temperature, Its Measurement and Control in Science and Industry, James F. Shooley, editor (American
Institute of Physics, New York), Vol. 6, Part 1 (1992).

c) Temperature, Its Measurement and Control in Science and Industry, James F. Shooley, editor (American
Institute of Physics, New York), Vol. 6, Part 2 (1992).

d) The International Temperature Scale of 1990, H. Preston-Thomas, Metrologia 27, 3 (1990).

e) The 1990 NIST Scales of Thermal Radiometry, Klaus D. Mielenz, Robert. D. Saunders, Albert C. Parr,
and Jack J. Hsia, J. Res. Natl. Inst. of Stds. Tech., 95, 621 (1990).

f) Spectroradiometric Determination of the Freezing Temperature of Gold, K. D. Mielenz, R. D.,
Saunders, J. B. Shumaker, J. Res. Natl. Inst. of Stds. Tech., 95, 49 (1990).

g) Temperature, T. J. Quinn (Academic Press, San Diego) (1990).

h)_ Theory and Practice of Radiation Thermometry, D. P. Dewitt and Gene D. Nutter, editors (John Wiley
and Sons, New York) (1988).

NIST Handbook 150-2E 13 August 2001


taking into account the relative uncertainties assigned by both the applicant and audit laboratories. NVLAP
employs the same principle used by the European Cooperation for Accreditation and described in EA-2/03
covering international measurement audits. Note that the objective is not to determine and certify the total
uncertainty of the applicant laboratory, as is done in a Measurement Assurance Program (MAP) with NIST,
but to verify (through the assessment process) that the uncertainty claimed by the applicant laboratory is
reasonable, and then to test that the measurement result obtained through the proficiency test is acceptable.

It is not the intention nor the mission of NVLAP to conduct MAPs or to otherwise provide traceability for
laboratories. Laboratories obtain these services from the NIST measurement divisions. NVLAP assesses
the implementation, application, and documentation of MAPs by laboratories. NVLAP accreditation
encourages the use of MAPs by the calibration laboratory community, and MAP results produce objective
evidence that NVLAP assessors look for as part of the assessment process.

1.7.2.3, Requirements

NVLAP's proficiency testing program uses a sampling approach. All applicant laboratories are required to
complete an annual proficiency test in one parameter under each field of calibration for which it has applied
to be accredited. For the purposes of the NVLAP Calibration Laboratories Accreditation Program, the
results of the proficiency test are considered as objective evidence, along with the on-site visit, of a
laboratory's ability to perform competent calibrations. Proficiency testing is conducted annually using
different parameters in each field; however, those laboratories accredited in only one parameter within a field
are retested in the same parameter.

1.7.2.4 Uncertainty determination

The applicant laboratory is required to perform a measurement or series of measurements on an artifact using
the same calibration method, apparatus, and personnel that it uses to calibrate customers’ equipment. The
laboratory must be able to identify and quantify all sources of uncertainty that affect the measurement. The
laboratory should attach an overall uncertainty to the measurement by combining all uncertainty
contributions, in their type A and type B components, in the root-sum-squared method as described in the
Guide to the Expression of Uncertainty in Measurement (see 1.4.1 (b)). The confidence limit used should
be k = 2, which is equivalent to a 95% confidence probability.

1.7.2.5 Pass/fail criteria

The performance of the proficiency test is judged by calculating the error of the measurement, normalized
with respect to the uncertainty of the measurement, using the following equation:

Ejormal =| (Value,,, - Value,,,) / ( Uncertainty,,, + Uncertainty,.,”)'” |
where

Enormal = Normalized error of the applicant laboratory
Value,,, = the value as measured by the applicant laboratory
Value,,., = the value as measured by the reference laboratory

Uncertainty,,,= the uncertainty of the reference laboratory
Uncertainty,,, = the uncertainty of the applicant laboratory

NIST Handbook 150-2E 7 August 2001


2.4.5.4 A laboratory that makes measurements of spectral flux and light source color should ideally use
an integrating sphere connected to a spectroradiometer and spectral flux standard lamps that are obtained
from or traceable to NIST. Other techniques may be used for less accurate measurements.

2.4.5.5 A laboratory that makes luminance measurements should have either standard sources or standard
photometers that are traceable to NIST. Standard sources can be integrating sphere sources or
transmitting/reflecting diffusers irradiated at known illuminance.

2.4.6  Calibration’methods

Laboratories may use the instrumentation and the test procedures described in the reference documents,
including the specific photometric and colorimetric procedures for each lamp type for which the laboratory
is seeking accreditation. Laboratories may use other well-derived and documented procedures.

2.4.7 Handling of calibration items

2.4.7.1 Care should be exercised when handling the lamps. Never touch the envelope of the lamp with
bare hands. Handle the lamp by its base or use gloves or a lint-free cloth when handling the envelope of the
lamp. Avoid mechanical shock to the lamps.

2.4.7.2 Incandescent lamps should be turned on and off slowly (for approximately 30 s each).
Incandescent lamps should not be moved while turned on. If a lamp must be moved during calibration, it
should be done carefully. Burning position of lamps should always be kept the same. Measurements should
be made only after the lamp has stabilized.

2.4.7.3. Discharge lamps should be operated with reference ballasts specified in the reference documents.
2.4.7.4 Measurements should be made only after the lamp has been stabilized for a sufficient period of
time depending on type of lamp (usually stabilization takes approximately 10 min for incandescent lamps
and 15 to 40 min for electrical discharge lamps).

2.4.8 Certificates and reports

2.4.8.1 | The report of calibration of lamps should include the operating condition of the lamps (current,
voltage, and other parameters as applicable), as well as photometric values.

2.4.8.2. The report of the luminous intensity calibration should include the reference point of the lamp,
alignment procedure, and the photometric distance used for the calibration.

2.4.8.3 The report of calibration of photometers should include the reference point of the photometer,
specification of light sources used, and the ambient temperature or photometer temperature at the calibration.

2.4.8.4 The reproducibility of photometric values of lamps (especially electrical discharge lamps) should
be included in the uncertainty of calibration.

NIST Handbook 150-2E 17 August 2001


the relevant requirements of ISO 9002 (ANSI/ASQC Q92-1987). These handbook criteria have been updated
to incorporate the requirements of ISO/IEC 17025:1999. The entire series of Handbooks 150-2A through
150-2H comprises information specific to the Calibration Laboratories Program and neither adds to nor
detracts from requirements contained in NIST Handbook 150.

Any questions or comments on this handbook should be submitted to the National Voluntary Laboratory

Accreditation Program, National Institute of Standards and Technology, 100 Bureau Drive, Stop 2140,
Gaithersburg, MD 20899-2140; phone (301) 975-4016; fax (301) 926-2884; e-mail NVLAP@nist.gov.

vi


i) Applications of Radiation Thermometry, Joseph C. Richmond and David P. Dewitt, editors (American
Society for Testing and Materials, Philadelphia) (1985).

j) Temperature, Its Measurement and Control in Science and Industry, (Instrument Society of America,
Pittsburgh) Vol. 4, Part 1 (1972).

k) Corrections in Optical Pyrometry and Photometry for the Refractive Index of Air, W. R. Blevin,
Metrologia, 8, 146 (1972).

1) Vacuum Tungstén Strip Lamps with Improved Stability as Radiance Temperature Standards:
Temperature, Its Measurement and Control in Science and Industry, T. J. Quinn and R. D. Lee
(Instrument Society of America, Pittsburgh: 1972) Vol. 4, Part 1, p. 395.

m) Intercomparison of the IPTS 68 Above 1064 °C by Four National Laboratories: Temperature, Its
Measurement and Control in Science and Industry, R. D. Lee, H. J. Kostkowski, T. J. Quinn, P. R.
Chandler, T. N. Jones, J. Tapping, and H. Kunz (Instrument Society of America, Pittsburgh, 1972) Vol.
4, Part 1, p. 377.

n) The NBS Photoelectric Pyrometer and Its Use in Realizing the International Practical Temperature
Scale above 1063 °C, R. D. Lee, Metrologia, 2, No. 4, 150 (Oct. 1966).

0) Theory and Methods of Optical Pyrometry, H. J. Kostkowski and R. D. Lee, National Bureau of
Standards (US), Monograph 41 (March 1962).

p) Temperature, Its Measurement and Control in Science and Industry (Instrument Society of America,
Pittsburgh), Vol. 3, Part 1 (1962).

2.3.3 Statistical process control

The laboratory should have reference and working standards that span the radiance temperature and spectral
range for the calibration service provided by the laboratory. At least two working standards, or a number
appropriate for the stated uncertainty, should be measured each time a test ribbon filament lamp or test
pyrometer is calibrated.

2.3.4 Accommodation and environment

The temperature and relative humidity of the laboratory environment should be monitored and reported in
the test report.

2.3.5 Equipment and reference materials

2.3.5.1 | The laboratory should maintain a reference standard ribbon filament lamp and/or pyrometer whose
radiance temperature calibration is obtained from or traceable to the National Institute of Standards and
Technology, other national laboratories, or intrinsic standards. This reference standard should span the
radiance temperature and spectral range for the calibration service provided by the laboratory. The accuracy
and stability of the reference standard should be verified at least annually.

2.3.5.2, The laboratory should maintain a group of at least three check standard ribbon filament lamps
and/or pyrometers whose radiance temperature calibration is traceable to the National Institute of Standards
and Technology, other national laboratories, or intrinsic standards through the laboratory's reference standard

NIST Handbook 150-2E 14 August 2001


2.6 Spectral radiance and spectral irradiance
2.6.1 Scope

This section contains specific technical criteria which a laboratory should meet if it is to be recognized as
competent to carry out spectral radiance or spectral irradiance calibrations.

2.6.2 References

a) NBS Measurement Services: Spectral Irradiance Calibrations, J. H. Walker, R. D. Saunders, J. K.
Jackson, and D. A. McSparron, National Bureau of Standards (U.S.), Special Publication 250-20 (Sept.
1987).

b) NBS Measurement Services: Spectral Radiance, J. H. Walker, R. D. Saunders, and A. T. Hattenburg,
National Bureau of Standards (U.S.), Special Publication 250-1 (Jan. 1987).

c) Spectral Irradiance Standard for the Ultraviolet: The Deuterium Lamp, R. D. Saunders, W. R. Ott, and
J. M. Bridges, Applied Optics 17, 593 (1978).

d) The 1973 NBS Scale of Spectral Irradiance, R. D. Saunders and J. B. Shumaker, National Bureau of
Standards (U.S.), Tech. Note 594-13 (1977).

e) High-Accuracy Spectral Radiance Calibration of Tungsten-Strip Lamps, H. J. Kostkowski, D. E.
Erminy, and A. T. Hattenburg, Adv. Geophys., 14, 111 (1970).

f) Methods of Characterizing the Performance of Radiometers and Photometers, 1982, CIE Publication
#53.

g) The Spectroradiometric Measurement of Light Sources, 1984, CIE Publication #63.

2.6.3 Statistical process control

The laboratory should have at least one reference standard lamp similar to the lamps calibrated by the
laboratory. The reference standard should span the spectral range for the calibration service provided by the
laboratory. Check standards should be measured each time calibration is done. The number of working
standards depends on the level of uncertainty.

2.6.4 Accommodation and environment

2.6.4.1 The temperature and humidity of the laboratory environment should be monitored and declared
in the test report.

2.6.4.2 When ultraviolet sources are used, UV eye protection and skin protection should be both worn by
the occupants of the room. Lasers should be shielded from direct eye view of the operator, and eye
protection rated for the class of laser should be worn.

NIST Handbook 150-2E 20 August 2001


f) IES Guide to Spectroradiometric Measurements, IES LM-58-94.

g) IES Approved Method for Electrical and Photometric Measurements of General Service Incandescent
Filament Lamps, LM-45-00.

h) IESNA Approved Method for the Electrical and Photometric Measurements of High Intensity Discharge
Lamps, LM-51-00 IESNA Approved Method for the Electrical and Photometric Measurements of High
Intensity Discharge Lamps, LM-51-00.

i) IESNA Guide for’the Measurement of Ultraviolet Radiation from Sources, LM-55-96.

j) The Basis of Physical Photometry, 1983, CIE Publication #18.2.

k) Methods of Characterizing Illuminance Meters and Luminance Meters, CIE Publication #69, (1987).

1) Measurement of Luminous Flux, CIE Publication #84, (1989).

m) Colorimetry, CIE Publication #15.2, 2nd ed., (1986).

2.43 Statistical process control

The laboratory should have control standards that adequately span the range of artifacts, wavelengths, and

intensities calibrated by the laboratory. Working standards should be measured each time calibration is done.

The number of working standards depends on the level of uncertainty.

2.4.4 Accommodation and environment

2.4.4.1 The temperature and humidity of the laboratory environment should be monitored and declared

in the test report. The ambient temperature of fluorescent lamps should be controlled to a nominal 25 °C

(+1 °C is recommended) during calibration.

2.4.4.2 Air draft variations should be considered and, if necessary, minimized or controlled, since they

could affect the output of electrical discharge lamps. They can be detected and analyzed by means ofa hot-

wire anemometer or other sensitive air movement instruments.

2.4.5 Equipment and reference materials

2.4.5.1 The laboratory should have standard measuring shunts, stable DC power supplies, high accuracy

digital voltage meters, stable mounting fixtures and other equipment necessary to make high accuracy

electrical and photometric measurements.

2.4.5.2 A laboratory that makes luminous intensity and/or illuminance measurements should have either

luminous intensity standard lamps or standard photometers which are traceable to NIST. Radiometric

standards can also be used with well-derived and documented procedures.

2.4.5.3 A laboratory that makes total luminous flux measurements normally uses an integrating sphere and

total luminous flux standard lamps which are traceable to NIST. Other methods, including use of

goniophotometers, can be used with photometric standards traceable to NIST and with well-documented
procedures.

NIST Handbook 150-2E 16 August 2001


c) Spectrophotometric measurements

1) Regular transmittance

2) Specular reflectance

3) 6°/hemispherical reflectance factor

4) 45°/0° reflectance factor

5) Coefficient of luminous intensity for retroreflectance
d) Spectral radiance and spectral irradiance measurements
e) Spectral responsivity measurements
f) Laser power and energy
g) Optical fiber power.

2.2.1.2 This material may be used as a guide by optical radiation calibration laboratories in the
development and implementation of their quality systems.

2.2.2 Statistical process control

2.2.2.1 All sources of variability for the calibration should be monitored by calibrating the subsystems and
through the use of check standards to ensure that the calibrations are carried out under controlled conditions.
The laboratory should maintain some form of statistical process control (SPC) commensurate with the
uncertainty levels of the calibration. The SPC control parameters should be based on measurements of check
standards (or closure parameters) and the repeatability of multiple measurements. The frequency and
number of process control checks should be appropriate for the number of calibrations, as well as the level
of uncertainty and reliability claimed for the calibration.

2.2.2.2 The laboratory should have control artifacts which adequately span the measurement range of
devices and samples normally calibrated by the laboratory. Every measured value of each control should
be recorded and compared to its historical value to determine that the process is in control. The comparison
may be made via a plotted control chart with appropriate control values, which should be updated at least
annually using the most current data.

2.2.3 Accommodation and environment

2.2.3.1 The laboratory should provide facilities for the effective monitoring, control, and recording of
environmental conditions. Attention should be paid to temperature, humidity, line voltage, dust,
electromagnetic interference, and vibrations.

2.2.3.2 Unless otherwise specified, the laboratory temperature should be controlled to a nominal of 23 °C
(4 2 °C is recommended), and the relative humidity should remain between 20 % and 60 %. The
temperature and humidity of the laboratory environment should be monitored and recorded.

NIST Handbook 150-2E i August 2001


c) ISO/IEC 17025: 1999: General requirements for the competence of testing and calibration laboratories.

d) ISO/IEC Guide 43: 1997, Proficiency testing by interlaboratory comparisons, Part I and Part 2.

e) ISO/IEC/BIPM International Vocabulary of Basic and General Terms in Metrology (VIM), 1993.
ISO documents b) through e) are available from:

Global Engineering Documents (paper copies)
Order phone: (800) 854-7179

American National Standards Institute (ANSI) (electronic copies)
Electronic Standards Store
ANSI web site: http://www.ansi.org

f) NIST Technical Note 1297, Guidelines for Evaluating and Expressing the Uncertainty of NIST
Measurement Results. Available on-line at http://physics.nist.gov/Document/tn1297 pdf.

g) EA-2/03, EA Interlaboratory Comparison (previously EAL-P7), Mar. 1996. Available on-line at
http://www.european-accreditation.org/.

h) ANSI/NCSL Z540-1-1994, Calibration Laboratories and Measuring and Test Equipment—General
Requirements.

i) ANSI/NCSL Z540-2-1997, U.S. Guide to the Expression of Uncertainty in Measurement.
j) NCSL Recommended Practice RP-7: Laboratory Design, 1993.
NCSL documents h) through j) available from:

NCSL International

1800 30" Street, Suite 305B

Boulder, CO 80301-1026

Phone: (303) 440-3339

Fax: (303) 440-3384

E-mail: info@neslinternational.org

Web site: http://www.ncslinternational.org

k)_ C.D.Ehrlichand S. D. Raspberry, “Metrological Timelines in Traceability,” Jour. Res. NIST, Vol. 103,
No. 1, Jan-Feb, 1998.

1) C. Croarkin, Measurement Assurance Programs, Part II: Development and Implementation, NBS
Special Publication 676-II (U.S. Government Printing Office, Washington, DC, 1985).

1.4.2 Additional references specific to optical radiation measurements are listed in Sections 2.3 through
2.9.

NIST Handbook 150-2E 3 August 2001


e) I. Vayshenker, X. Li, D. Livigni, T. R. Scott, C. L. Cromer, "Optical Fiber Power Meter Calibrations
at NIST," NIST SP 250-54, 36 pp (June 2000).

2.9.3 Statistical process control

The laboratory should have at least two working standard detectors that span the spectral and power ranges
of the detectors calibrated by the laboratory. At least one working standard should be measured each time
a sample is calibrated.

2.9.4 Accommodation and environment
2.9.4.1 The temperature and humidity of the laboratory environment should be monitored and recorded.

2.9.4.2 Appropriate eye protection and shielding should be used when lasers are in use. Other safety
hazards should be properly handled (e.g., proper ventilation for toxic gases, etc.).

2.9.5 Equipment and reference materials

2.9.5.1 | The laboratory should maintain a thoroughly characterized primary standard whose calibration is
traceable to NIST on an annual basis or in support of the laboratory's stated uncertainty. This calibration
should be performed at the wavelengths, power/energy ranges, and input modes (i.e., parallel beam or
connectorized fiber) to be used in the calibration services provided by the laboratory and commensurate with
the uncertainty and device design.

2.9.5.2. The laboratory should maintain a minimum of two working detectors whose response
characteristics are traceable to NIST through the laboratory primary standard. The responses of these
working standards should be characterized at the wavelengths, power/energy ranges, and input modes (i.e.,
parallel beam or connectorized fiber) to be used in the calibration services provided by the laboratory.

2.9.6 Calibration methods

2.9.6.1 The test detectors should be calibrated by comparison to the working detectors at the appropriate
wavelength, power/energy, and input mode.

2.9.6.2 The dependency of the device response on the calibration source wavelength should be considered.
2.9.7 Handling of calibration items

2.9.7.1 If appropriate, the test detectors should be kept in their shipping containers until ready for testing.
Care should be exercised when handling the test detectors, especially not to touch their windows or bare
active areas. If necessary, a test detector window can be cleaned with lens tissue and spectral grade solvent.
Optical fiber ends should be inspected and cleaned as appropriate. Before calibration begins, the test detector
should be allowed sufficient time to reach equilibrium with the laboratory environment.

2.9.7.2. Alternately, the test detectors can be kept in a dust-free enclosure that is maintained at the same
temperature and humidity levels as the laboratory.

NIST Handbook 150-2E 26 August 2001


the spectral range of the calibration service provided by the laboratory. The working standard(s) should be
verified by comparison to the reference standard on an appropriate schedule. The reference standard detector
may be used as the working standard when justified by the calibration workload.

2.7.6 Calibration methods

Calibration methods should consist of well-documented and established techniques that are reviewed
periodically to embody accepted laboratory practices.

2.7.7 Handling of calibration items

2.7.7.1 Care should be exercised when handling the test detectors, especially not to touch their windows
or bare active areas. In the event that the detector or radiometer is equipped with a precision aperature, the
inside edge of the precision aperture is extremely delicate and should not be touched with fingers or any
other object. Some test detector windows can be cleaned with lens tissue and spectral grade solvent. The
precision aperture should be removed before cleaning the detector window (if possible).

2.7.7.2 Some detector surfaces, especially bare surfaces, can absorb moisture and should be stored
appropriately.

2.7.8 Certificates and reports

2.7.8.1 The report should describe the methodology and instrumentation used to determine the spectral
response.

2.7.8.2. The report should indicate the spectral responsivity versus wavelength and measurement
uncertainties.

2.8 Laser power and energy

2.8.1 Scope

This section contains specific technical criteria which a laboratory should meet if it is to be recognized as
competent to carry out laser power and energy calibrations of laser radiation detectors and meters (referred
to as "detectors" throughout the remainder of this section).

2.8.2 References

a) W.E. Case, "Documentation of the NBS C, K, and Q Laser Calibration Systems," Natl. Bur. Stand.
(U.S.), NBSIR 82-1676 (Sept. 1982).

b) T. R. Scott, "NBS Laser Power and Energy Measurements," Proc. S SPIE O-E LASE '88,
Optoelectronics and Laser Applications in Science and Engineering (1988).

c) A.A. Sanders and A. L. Rasmussen, "A System for Measuring Energy and Peak Power of Low-Level
1.064 jum Laser Pulses," Natl. Bur. Stand. (U.S.), Tech. Note 1058 (Oct. 1982).

NIST Handbook 150-2E 23 August 2001


Summary

This guide presents the general technical requirements (i.e., on-site assessment and proficiency testing) of
the laboratory accreditation program for calibration laboratories along with specific technical criteria and
guidance applicable to optical radiation measurement. These technical guidelines are presented to indicate
how the NVLAP criteria may be applied.

Any calibration laboratory (including commercial, manufacturer, university, or federal, state, or local
government laboratory) engaged in calibration in optical radiation frequency measurements listed in this
handbook may apply for NVLAP accreditation. Accreditation will be granted to a laboratory that complies
with the criteria for accreditation as defined in NIST Handbook 150. Accreditation does not guarantee
laboratory performance ~ it is a finding of laboratory competence.

Fields of calibration covered: Specific calibration parameters and related stimulus and measurement
devices in areas of optical radiation.

Scope of accreditation: Calibration parameter(s), range, and uncertainty level. Types of measuring and test
equipment. Quality assurance system for measuring and test equipment.

Period of accreditation: One year, renewable annually.

On-site assessment: Visit by an assessor(s) to determine compliance with the NVLAP criteria before initial
accreditation, in the first renewal year, and every two years thereafter. Preassessment and monitoring visits
as required. All calibration parameters or general areas of calibration within the specific scope of
accreditation requested will be assessed.

Assessors: Selected from technical experts with experience in the appropriate areas of calibration and
quality systems assessment.

Proficiency testing (measurement assurance): Each laboratory is required to demonstrate its capability to
successfully perform calibrations as part of on-site assessment or by documented successful completion of
an approved Measurement Assurance Program (MAP) or round-robin correlation. Proficiency testing may
be required for initial accreditation, or where other evidence of measurement assurance is not evident, and
may be conducted annually thereafter. Advance notice and instructions are given before proficiency testing
is scheduled.

Fees: Payments are required as listed on the NVLAP fee schedule, including the initial application fee,
administrative/technical support fee, on-site assessment fee, and proficiency testing fee.

viii


Acknowledgments

NIST Handbook 150-2 was first available as a draft covering all eight fields of physical metrology
calibration in one volume. It has been separated into eight handbooks to allow easier updating and electronic
downloading from the NVLAP web site. The preparation of these documents has been a joint effort, with
input from representatives of other government agencies, laboratories, and the private sector.
Acknowledgment of their efforts is in order; however, the listing of individual names is impractical. The
submissions by individuals and companies offering suggestions for improvement to this document were also
very welcome, as were the contributions of those who attended the public workshops.

We thank all the NIST measurement divisions for their work in writing or contributing to the individual
handbooks. Listed below are those from the NIST measurement divisions who deserve special thanks for
input to Handbook 150-2E, Technical Guide for Optical Radiation Measurements:

Dr. Ted Early and Dr. Maria Nadal (Spectrophotometry), Charles E. Gibson (Radiance
Temperature, Spectral Radiance and Spectral Irradiance), Sally S. Bruce and Thomas C. Larason
(Spectral Responsivity), Dr. Yoshihiro Ohno (Photometry), and Thomas R. Scott (Laser Power and
Energy and Optical Fiber Power). Editing and Coordination: Sally S. Bruce and Dr. Keith Lykke.

Additional thanks go to those who actively participated in the Technical Guide Workshop held November
1993 and to those who served as points of contact within fields of calibration. They include: Georgia L.
Harris, Norman B. Belecki, Dr. Theodore D. Doiron, Robert M. Judish, Thomas C. Larason, Sally S. Bruce,
and Dr. Donald B. Sullivan. A special thanks is owed to James L. Cigler for work in developing the content
and format of this guide, and to Vanda White for her editorial expertise in making this a readable document.

Above all, we wish to thank Jon M. Crickenberger, the editor of the first three drafts of this document, for
literally hundreds of hours of his work in creating this guide. It was he who tasked the contributors to
produce the technical content, assembled the results of their efforts into a consistent format, and provided
the general commentary. Without Jon's dedicated effort to this monumental task, this guide would never
have been published.

NVLAP has edited the individual handbooks and made changes resulting from comments by individuals to
earlier draft versions. This editing has been to a different extent for each parameter. Every effort was made
to include all pertinent information relevant to an ISO/IEC 17025-derived technical guide.

C. Douglas Faison and Carroll S. Brickenkamp, Editors
National Voluntary Laboratory Accreditation Program
National Institute of Standards and Technology

100 Bureau Drive, Stop 2140

Gaithersburg, MD 20899-2140

vii


2.2.4 Equipment and reference materials

2.2.4.1 The laboratory should be furnished with all items of equipment for the correct performance of
optical radiation calibrations.

2.2.4.2. The laboratory should have appropriately clean storage areas for storing reference materials.
2.2.5 Handling of calibration items

2.2.5.1 Calibration items should be inspected for damage and completeness when received and stored in
an appropriately clean and safe place when not in use.

2.2.5.2 Detectors, sources, and reference materials should be cleaned when necessary.

2.2.6 Calibration methods

The laboratory should have documented calibration procedures to be followed for each type of calibration.
2.2.7 Records

2.2.7.1 All data associated with a measurement should be recorded, stored, and kept for a period of time
as stated in the quality manual. If corrections are applied, the worksheets should show the measurement
data, corrections, and final answers. The temperature, humidity, date, identification of test material and

controls, and other pertinent process information should be included.

2.2.7.2 Information relating to the procedures, equipment, standards, results, and personnel involved for
a particular calibration should be maintained for the period of time stated in the quality manual.

2.2.7.3 Records associated with a particular standard or control should be kept for the period of time stated
in the quality manual.

2.2.8 Certificates and reports

2.2.8.1 The content of all certificates or reports of calibration must meet the requirements of NIST
Handbook 150. SI units should be used unless otherwise required by the customer.

2.2.8.2 All certificates or reports of calibration should contain an uncertainty statement which is based
upon scientifically determined data and which agrees with the laboratory's stated best uncertainty definition.

2.2.8.3. The uncertainty determination should follow the methods described in the ISO Guide to the
Expression of Uncertainty in Measurement and be derived from a model of the measurement system which
includes (as applicable) the uncertainties caused by:

a) Master artifact calibration

b) Long-term reproducibility of measurement system

c) Instrument geometry

1) Alignment of the test material to the source

NIST Handbook 150-2E 12 August 200]


On September 18, 1992, a public workshop was held at NIST Gaithersburg and attended by a mix of private
sector and government personnel. The workshop reviewed a draft handbook, which included general
requirements, as well as very specific technical requirements for de voltage calibrations at all levels. As a
result of the workshop, the draft handbook was revised to take the form of a Calibration Laboratories
Program Handbook, which included the general requirements for laboratories (using ISO/IEC Guide 25 as
a basis), and eight companion Technical Guides covering the specific requirements for each field of
calibration offered for accreditation.

On May 18, 1993, a public workshop on the revised draft program handbook was held at NIST Boulder and
attended by more than’60 industry and government personnel. Comments from this workshop, as well as
responses to a survey/checklist mailing, were used to prepare the final draft of the handbook, now entitled
NVLAP Procedures and General Requirements (NIST Handbook 150), published in March 1994. [A revised
NIST Handbook 150 incorporating ISO/IEC 17025:1999 is dated 2001.]

A public workshop for the Calibration Laboratories Technical Guides was held at NIST Gaithersburg, on
November 22 through 24, 1993. More than 60 industry and government personnel attended and provided
comments on the draft version of the Technical Guide for each of eight fields of calibration. Asa result, the
eight Technical Guides were incorporated into a draft Handbook 150-2, Calibration Laboratories Technical
Guide, covering the fields being offered for accreditation. [In 2000, Handbook 150-2 (draft) was divided into
eight handbooks, one for each calibration area.]

The need for technical experts to serve as assessors was advertised, and the first group of assessors was
selected and trained during a four-day session held from November 16 through 19, 1993, in Gaithersburg,
using materials developed by NVLAP.

The Calibration Laboratories Accreditation Program officially began accepting applications when
notification was given in the Federal Register dated May 11, 1994. Applications are accepted and processed
in accordance with procedures found in NIST Handbook 150.

1.4 References
1.4.1 The following documents are referenced in this handbook.
a) NIST Handbook 150, NVLAP Procedures and General Requirements; available from:

National Voluntary Laboratory Accreditation Program
National Institute of Standards and Technology

100 Bureau Drive, Stop 2140

Gaithersburg, MD 20899-2140

Phone: (301) 975-4016

Fax: (301) 926-2884

E-mail: nvlap@nist.gov

NVLAP Web site: http://www.nist.gov/nvlap

b) ISO/IEC/BIPM (BIPM is the Bureau International des Poids et Mesures, the International Bureau of
Weights and Measures) Guide to the Expression of Uncertainty in Measurement (GUM), 1993.

NIST Handbook 150-2E 2 August 2001


2.5 Spectrophotometry

2.5.1 Scope

This section contains specific technical criteria which a laboratory should meet and demonstrate if it is to
be recognized as competent to carry out spectrophotometric calibrations in the following parameters:
Regular Transmittance, Specular Reflectance, 6°/Hemispherical Reflectance Factor, 45°/0° Reflectance
Factor.

2.5.2 References

a) P.Y. Barnes, E.A. Early, and A.C. Parr, "NIST Measurement Services: Spectral Reflectance," NIST
Special Publication 250-8 (1998).

b) KL. Eckerle, J.J. Hsia, K.D. Mielenz, V.R. Weidner, NBS Measurement Services: Regular Spectral
Transmittance, NBS Special Publication 250-6 (1987).

c) NBS Measurement Services: Spectral Reflectance, V. R. Weidner and J. J. Hsia, National Bureau of
Standards (U.S.), Special Publication 250-8 (July 1987).

d) National Scales of Spectrometry in the U.S., J. J. Hsia, Advances in Standards and Methodology in
Spectrophotometry 1987, Elsevier Science Publishers, B. V., Amsterdam, pp. 99-109 (1987).

e) Measurement Assurance Program Transmittance Standards for Spectrophotometric Linearity Testing:
Preparation and Calibration, J. Res. Natl. Bur. Std. 88 25 (Jan.-Feb. 1983).

f) Radiometric and Photometric Characteristics of Materials and their Measurement, 1977, CIE
Publication #38.

g) Absolute Methods for Reflection Measurements, 1979, CIE Publication #44.

h) A Review of Publications on Properties and Reflection Values of Material Reflection Standards, 1979,
CIE Publications #46.

i)  Recalibration of the NBS Glass Standards of Spectral Transmittance, J. Res. Natl. Bur. Std. (U.S.) 67A,
577 (1963).

j) NBS Research Paper RP 2093, Permanence of Glass Standards of Spectral Transmittance, J. Res. Natl.
Bur. Std. (U.S.) 44, 463 (1950).

2.5.3 Statistical process control

The laboratory should have working standards that span the specific spectrophotometric measurement
calibrated by the laboratory. Standards of the type to characterize measurement process, intensities, and
wavelength region should be measured each time calibration is performed. Records of measurement
parameters and results should be kept.

NIST Handbook 150-2E 18 August 2001


NIST HANDBOOK 150-2E

National
Voluntary
Laboratory
Accreditation
Program

Calibration
Laboratories

Technical Guide

for
Optical Radiation
Measurements

C. Douglas Faison and
Carroll S. Brickenkamp, Editors

August 2001

nT OF Coy,

& S

38

Ss
Wen y 2

En,

*
yan #0.
°

on
States of TM

U.S. Department of Commerce
Donald L. Evans, Secretary

Technology Administration
Karen H. Brown, Acting Under Secretary for
Technology

National Institute of Standards and Technology
Karen Brown, Acting Director


of customer laboratories and/or if decided by NVLAP to be in the best interest of the Calibration
Laboratories program.

The laboratory is requested to indicate on the Fields of Calibration/Parameters Selection List the
parameter(s) for which accreditation is desired, along with appropriate ranges and uncertainties. There is
also provision for an applicant laboratory to request accreditation for parameters not currently listed on the
Selection List, or for accreditation of the quality system employed for assuring Measurement and Test
Equipment (M & TE) used in support of product certification. Request for accreditation of quality assurance
systems for M & TE will be treated as a separate field of calibration for the purpose of setting appropriate
fees. Once a laboratory meets all the requirements for accreditation for the Fields of Calibration/Parameters
Selection List, this information will become the basis for the Scope of Accreditation document.

1.6.3 Checklists

Checklists enable assessors to document the assessment of the laboratory against the NVLAP requirements
found in NIST Handbook 150. The NVLAP Calibration Laboratories Accreditation Program incorporates
the NVLAP General Operations Checklist. The questions are applicable to evaluating a laboratory's ability
to operate a calibration program, and address factors such as the laboratory's organization, management, and
quality system in addition to its calibration competency.

The NVLAP General Operations Checklist is numbered to correspond to the requirements in NIST
Handbook 150. Comment sheets are used by the assessor to explain deficiencies noted on the checklist.
Additionally, the assessor may use the sheets to make comments on aspects of the laboratory's performance
other than deficiencies.

1.7 Assessing and evaluating a laboratory

1.7.1 On-site assessment

1.7.1.1 The NVLAP lead assessor will schedule with the laboratory the date for on-site evaluation, and
will request the quality manual and documented quality and calibration procedures in advance of the visit
to reduce time spent at the laboratory; such materials will be returned by the assessor. NVLAP and the
assessor will protect the confidentiality of the materials and information provided. The laboratory should
be prepared to conduct routine calibrations, have equipment in good working order, and be ready for
examination according to the guidance contained in this handbook, the requirements identified in NIST
Handbook 150, and the laboratory's quality manual. The assessor will need time and work space to complete
assessment documentation while at the laboratory, and will discuss these needs at the opening meeting of
the on-site assessment.

1.7.1.2. NVLAP technical assessors are provided with the NVLAP General Operations Checklist to help
ensure the completeness, objectivity, and uniformity of the on-site assessment.

1.7.1.3. When accreditation has been requested for a considerable number of fields of calibration and
parameters, the assessment may range from observing calibrations in progress, requiring repeat
measurements on completed calibrations, to listening to laboratory staff describe the calibration process.
The depth into which the assessor performs the assessment depends on the number of fields of calibration
and associated parameters for which accreditation is requested and the time required to perform a given
calibration.

NIST Handbook 150-2E 5 August 2001


1.5 Definitions

Definitions found in NIST Handbook 150 apply, but may be interpreted differently or stated differently,
when necessary to amplify or clarify the meaning of specific words or phrases as they apply to specific
technical criteria.

15.1 Proficiency Testing: Determination of laboratory performance by means of comparing and
evaluating calibrations or tests on the same or similar items or materials by two or more laboratories in
accordance with predetérmined conditions. For the NVLAP Calibration Laboratories Accreditation Program,
this entails using a transport standard as a measurement artifact, sending it to applicant laboratories to be
measured, and then comparing the applicant's results to those of a reference laboratory on the same artifact.

1.5.2 Traceability: Property of the result of a measurement or the value of a standard whereby it can
be related to stated references, usually national or international standards, through an unbroken chain of
comparisons all having stated uncertainties. [VIM:1993, 6.10]

A single measurement intercomparison is sufficient to establish uncertainty relationships only over a limited
time interval (see reference 1.4.1.(k)); internal measurement assurance (see reference 1.4.1(1)), using control
(check) standards, is required to fully demonstrate that uncertainties remain within stated levels over time.
For the purposes of demonstrating traceability for NVLAP accreditation, a laboratory must demonstrate not
only that there is an unbroken chain of comparisons to national standards, but also that this chain is supported
by appropriate uncertainties, measurement assurance, continuous standard maintenance, proper calibration
procedures, and handling of standards. In this way, traceability is related to these other areas of calibration.

1.6 NVLAP documentation
1.6.1 Accreditation documents

Laboratories granted NVLAP accreditation are provided with two documents: Scope of Accreditation and
Certificate of Accreditation.

The Scope of Accreditation lists the "Best Uncertainty" that an accredited laboratory can provide for a given
range or nominal value within a given parameter of measurement. This "Best Uncertainty" is an statement
of the smallest uncertainty that a laboratory has been assessed as capable of providing for that particular
range or nominal value. The actual reported value of uncertainty for any particular measurement service that
the accredited laboratory provides under its scope may vary depending on such contributors as the statistics
of the test and uncertainties associated with the device under test.

1.6.2 Fields of calibration/parameters selection list

The Calibration Laboratories program encompasses eight fields of physical metrology calibration, with
multiple parameters under each field. Each field is covered by a separate handbook (NIST Handbooks 150-
2A through 150-2H). (Fields of accreditation under Chemical Calibration are covered by separate
handbooks.) Depending on the extent of its calibration capabilities, a laboratory may seek accreditation to
all or only selected fields and parameters within the scope of the program. The fields of calibration and their
related parameters are given on the Fields of Calibration and Parameters Selection List, which is provided
to a laboratory seeking accreditation as part of the NVLAP application package for the program. Additional
fields of calibration and/or parameters may be added to the Calibration Laboratories program upon request

NIST Handbook 150-2E 4 August 2001


2.8.7 Handling of calibration items

2.8.7.1 Ifappropriate, the test detectors should be kept in their shipping containers until ready for testing.
Care should be exercised when handling the test detectors, especially not to touch their windows or bare
active areas. If necessary, a test detector window can be cleaned with lens tissue and spectral grade solvent.
Before calibration begins, the test detector should be allowed sufficient time to reach equilibrium with the
laboratory environment.

2.8.7.2 Alternatively, the test detectors can be kept in a dust-free enclosure that is maintained at the same
temperature and humidity levels as the laboratory.

2.8.8 Certificates and reports

2.8.8.1 The report should describe the method and associated instrumentation used to determine the
response of the test detector to a measured amount of laser radiation input. This description should include
all pertinent information concerning the test detector (such as power/energy range, wavelength setting, etc.).
2.8.8.2 The report should give the average output response of the test detector relative to the power/energy
incident onto the detector at the power/energy levels and wavelengths used in the calibration. The report
should also include information on the bias condition on the detector.

2.8.8.3. The report should give the associated measurement uncertainty for each calibration number

provided for the test detector. The report should describe the pertinent uncertainty components and the
method used to combine these factors into a single uncertainty.

2.9 Optical fiber power

2.9.1 Scope

This section contains specific technical criteria which a laboratory should meet if it is to be recognized as
competent to carry out fiber optic power calibrations of detectors and power meters (referred to as
"detectors" throughout the remainder of this section).

2.9.2 References

a) X. Li and R. L. Gallawa, "Calibrated Optical Fiber Power Meters: Errors Due to Variations in
Connectors," Fiber and Integrated Optics, Vol. 7 (Mar. 1988).

b) R.L. Gallawa and X. Li, "Calibration of Optical Fiber Power Meters: The Effect of Connectors," Appl.
Opt. 26, 1170 (Apr. 1987).

c) R.L. Gallawa and S. Yang, "Optical Fiber Power Meters: A Round Robin Test of Uncertainty," Appl.
Opt. 25, 1066 (Apr. 1986).

d) I. Vayshenker, S. Yang, X. Li, T. R. Scott, C. L. Cromer, "Optical Fiber Power Meter Nonlinearity
Calibrations at NIST," NIST SP 250-56, 29 pp (Aug. 2000).

NIST Handbook 150-2E 25 August 2001


d) P.A. Simpson, "A System for Measuring the Characteristics of High Peak Power Detectors of Pulsed
CO, Radiation," Natl. Bur. Stand. (U.S.), Tech. Note 1023 (Sept. 1980).

e) E.D. West,"A System for Calibrating Laser Power Meters for the Range 5-1000 W," Natl. Bur. Stand.
(U.S.), Tech. Note 685 (May 1977).

f) A.A. Sanders and A. R. Cook, "An NBS Measurement Assurance Program," Proc. Electro-Optics Laser
Conference (1976).

g) D.L. Franzen and’L. B. Schmidt, "Absolute Reference Calorimeter for Measuring High-Power Laser
Pulses," Appl. Opt. 15, 3115 (Dec. 1976).

h)_ E. D. West, W. E. Case, A. L. Rasmussen, and L. B. Schmidt, "A Reference Calorimeter for Laser
Energy Measurement," J. Res. Natl. Bur. Stand. (U.S.), 76A, No. 1, 13 (Jan.-Feb. 1972).

i) J. H. Lehman, "Calibration Service for Spectral Responsivity of Laser and Optical-Fiber Power Meters
at Wavelengths Between 0.4 mm and 1.8 mm," NIST SP 250-53, 39 pp (Dec. 1999).

2.8.3 Statistical process control

The laboratory should have at least two working standard detectors that span the spectral and power ranges
of the detectors calibrated by the laboratory. At least one working standard should be measured each time
a sample is calibrated.

2.8.4 Accommodation and environment

2.8.4.1 The temperature and humidity of the laboratory environment should be monitored and recorded.

2.8.4.2 Appropriate eye protection and shielding should be used when lasers are in use. Other safety
hazards should be properly handled (e.g., proper ventilation for toxic gases, etc.).

2.8.5 Equipment and reference materials

2.8.5.1 The laboratory should maintain a thoroughly characterized primary standard whose calibration is
traceable to NIST. This calibration should be performed at the wavelengths, power/energy ranges, and
temporal modes (i.e., cw or pulsed) to be used in the calibration services provided by the laboratory.

2.8.5.2. The laboratory should maintain a minimum of two working detectors whose response
characteristics are traceable to NIST through the laboratory primary standard. The responses of these
working standards should be characterized at the wavelengths, power/energy ranges, and temporal modes
(i.e., ew or pulsed) to be used in the calibration services provided by the laboratory.

2.8.5.3 The laboratory should have the appropriate instrumentation for transferring the calibration at the
wavelengths, power/energy ranges, and temporal modes of the calibration service provided by the laboratory.

2.8.6 Calibration methods

The test detectors should be calibrated by comparison to the working detectors at the appropriate wavelength,
power/energy, temporal mode, and power density.

NIST Handbook 150-2E 24 August 2001


1 General information
1.1 Purpose

The purpose of this handbook is to amplify the general requirements for accreditation by NVLAP of
calibration laboratories in the area of optical radiation measurements covered by the Calibration Laboratories
Program. It complements and supplements the NVLAP programmatic procedures and general requirements
found in NIST Handbook 150, NVLAP Procedures and General Requirements. The interpretive comments
and additional guidelines contained in this handbook make the general NVLAP criteria specifically
applicable to the Calibration Laboratories Program.

This handbook does not contain the general requirements for accreditation, which are listed in NIST
Handbook 150, but rather provides guidelines for good calibration laboratory practices, which may be useful
in achieving accreditation.

1.2 Organization of handbook

The handbook is organized in two sections. The first section provides additional explanations to the general
procedures and requirements contained in NIST Handbook 150. The second section provides details and
guidance very specific for optical radiation calibration laboratories.

1.3 Description of Calibration Laboratories Accreditation Program

On May 18, 1992, as a result of the petition and public notice process, the Director of the National Institute
of Standards and Technology published in the Federal Register a notice of intent to develop the Calibration
Laboratories Accreditation Program under the procedures of the National Voluntary Laboratory
Accreditation Program . On June 2, 1994, the procedures and general requirements under which NVLAP
operates, Title 15, Part 285 of the U.S. Code of Federal Regulations (CFR), were revised to:

a) expand the procedures beyond testing laboratories to include accreditation of calibration laboratories,

b) update the procedures to ensure compatibility with generally accepted conformity assurance and
conformity assessment concepts,

c) incorporate international changes, especially with relevant International Organization for
Standardization/International Electrotechnical Commission (ISO/IEC) documents (e.g., ISO/IEC Guides
25 (now ISO/IEC 17025:1999), 38, 43, and 58, and the ISO 9000 series), and

d) facilitate and promote acceptance of the calibration and test results between countries to avoid barriers
to trade.

Calibration laboratory accreditation is offered in eight fields of physical metrology calibration covering a
wide variety of parameters and includes accreditation in multifunction measuring and test equipment
calibrations. Specific requirements and criteria have been established for determining laboratory
qualifications for accreditation following prescribed NVLAP procedures. The criteria address quality
systems, staff, facilities and equipment, test and calibration methods and procedures, manuals, records, and
calibration/certification reports.

NIST Handbook 150-2E 1 August 2001


lamp and/or pyrometer. These check standards should span the radiance temperature and spectral range for
the calibration service provided by the laboratory. The accuracy and stability of the check standards should
be verified by comparison to the reference standard in support of the laboratory’s uncertainty requirements.

2.3.6 Calibration methods

2.3.6.1 Test pyrometers may be calibrated by comparison to a standard pyrometer, by measurement of a
standard ribbon filament lamp, using blackbody techniques, or other well derived calibration methods.

2.3.6.2 Test ribbon ‘filament lamps are to be calibrated by spectral comparison to a standard ribbon
filament lamp, by measurement witha standard pyrometer, using blackbody techniques, or other well derived
calibration methods.

2.3.7 Handling of calibration items

The test lamp should be handled by the lamp base. Care should be exercised when handling the ribbon
filament lamps, and the envelope of the lamp should not be touched with bare hands. Gloves or a lint-free
cloth should be used when handling the envelope of the lamp to mount the test lamp in a socket. Care should
be taken to avoid shock and vibration to the lamp.

2.3.8 Certificates and reports

2.3.8.1 The calibration report for a pyrometer should give the radiance temperatures of the reference and
the radiance temperatures measured by the test pyrometer.

2.3.8.2 The calibration report for a ribbon filament lamp should give the radiance temperatures, test
current, and voltage across the filament of the test ribbon filament lamp.

2.4 Photometry

2.4.1 Scope

This section contains specific technical criteria which a laboratory should meet if it is to be recognized as
competent to carry out photometric calibrations.

2.4.2 References

a) NIST Measurement Services: Photometric Calibrations, Y. Ohno, NIST Special Publication 250-37
(July 1997).

b) Photometry, J. W. T. Walsh, 3rd edition, Constable, London, 1958.

c) IES Guide for the Selection, Care and Use of Electrical Instruments in the Photometric Laboratory, IES
LM-28-1989.

d) IES Approved Method for the Electrical and Photometric Measurements of Fluorescent Lamps, IES
LM-9-1999,

e) IES Practical Guide to Colorimetry of Light Sources, IES LM-16-84.

NIST Handbook 150-2E 15 August 2001


2.6.5 Equipment and reference materials

2.6.5.1 The laboratory should maintain a reference standard lamp whose spectral radiance or spectral
irradiance calibration is obtained from or traceable to the National Institute of Standards and Technology
or another national laboratory, or intrinsic standards.

2.6.5.2 The laboratory should have standard measuring shunts, stable DC power supplies, high accuracy
digital voltage meters, stable mounting fixtures, and other equipment necessary to make high accuracy
spectroradiometric measurements.

2.6.5.3. The laboratory should have the equipment and expertise to measure and quantify possible
measurement errors.

2.6.6 Calibration methods

2.6.6.1 Polarity of lamp currents should be maintained throughout their measurements. Laboratories
should have the capability to set and/or reproduce source electrical operating parameters.

2.6.6.2 At least three working standards should be used for each calibration. Less than three working
standards may be used depending on the level of uncertainty.

2.6.6.3 At least three measurements should be made on each source to maintain statistical control of the
process.

2.6.7 Handling of calibration items

2.6.7.1 The test lamps should be handled by the lamp base. Care should be exercised when handling the
lamps; do not touch the envelope of the lamp with bare hands. Gloves or a lint-free cloth should be used
when handling the envelope of the lamp to mount the test lamp in a socket. Avoid mechanical shock to the
filament of the lamp.

2.6.7.2 The lamps should be turned on and off slowly (for approximately 30 s each time). Measurements
should be made only after the lamp has stabilized (approximately 20 min after the lamps are turned on).

2.6.8 Certificates and reports
The calibration report should provide the spectral radiance or spectral irradiance versus wavelength, the lamp
current, and the lamp voltage. Measurements are reported for specific lamp orientation and current. If

necessary, documentation is included to interpolate data at wavelengths other than those reported. This does
not apply to fluorescent lamps.

2.7 Spectral responsivity
2.71 Scope
This section contains specific technical criteria which a laboratory should meet if it is to be recognized as

competent to carry out spectral responsivity calibrations of optical radiation detectors (referred to as
"detectors" throughout the remainder of this section).

NIST Handbook 150-2E 21 August 2001


Preface

The Calibration Laboratories Accreditation Program was developed by the National Voluntary Laboratory
Accreditation Program (NVLAP) at NIST as a result of interest from private industry and at the request of
the National Conference of Standards Laboratories. The goal of the program is to provide a means by which
calibration laboratories can be assessed for competency. This voluntary program is not designed to serve as
a means of imposing specific calibration procedures or minimum uncertainties on applicant laboratories;
instead, the program allows for all scientifically valid calibration schemes and requires that laboratories
derive and document their measurement uncertainties.

To accomplish this goal, NVLAP employs technical experts, on a contract basis, to serve as assessors in each
of the following eight fields of physical metrology calibration:

+ electromagnetic dc/low frequency,

+ electromagnetic rf/microwave frequency,
* time and frequency,

* ionizing radiation,

* optical radiation,

« dimensional,

* mechanical, and

+ thermodynamics.

NIST Handbooks 150-2A through 150-2H are technical guides for the accreditation of calibration
laboratories, with each handbook corresponding to one of the eight fields of physical metrology calibration.
They are intended for information and use by:

* NVLAP technical experts in assessing laboratories,

+ staff of accredited laboratories,

* those laboratories seeking accreditation,

+ other laboratory accreditation systems,

+ users of laboratory services, and

+ others needing information on the requirements and guidelines for accreditation under the NVLAP
Calibration Laboratories Accreditation Program.

NOTE The Calibration Laboratories Accreditation Program has been expanded to cover chemical calibration for
the providers of proficiency testing and certifiers of spectrophotometric NTRMs. (See NIST Handbooks 150-19 and
150-21.) Other NVLAP handbooks in the chemical calibration area are expected in the future.

The assessor uses NIST Handbook 150, NVLAP Procedures and General Requirements, and the appropriate
guides (NIST Handbooks 150-2A through 150-2H) to validate that a laboratory is capable of performing
calibrations within the laboratory’s stated uncertainties. These technical guides and other relevant technical
information support assessors in their assessments of laboratories. Along with inspecting the facilities,
documentation, equipment, and personnel, the assessor can witness a calibration, have an item recalibrated,
and/or examine the results of measurement assurance programs and round-robins to collect objective
evidence.

NIST Handbooks 150-2A through 150-2H supplement NIST Handbook 150, which contains Title 15 of the
U.S. Code of Federal Regulations (CFR) Part 285 plus all general NVLAP procedures, criteria, and policies.
The criteria in NIST Handbook 150 originally encompassed the requirements of ISO/IEC Guide 25:1990 and


To pass the proficiency test, the applicant laboratory must have a value for E,,,,4 less than 1 (i.€., Exma <1).
The results may be plotted graphically, with lines representing the limits of uncertainty of the measurements.

The anonymity of each applicant laboratory will always be preserved.
1.7.2.6 Scheduling and handling

Proficiency testing is scheduled by NVLAP-designated reference laboratories. These sites are NIST
laboratories or NVLAP-accredited laboratories that have been found to have the ability to perform the
required proficiency tests to an uncertainty level appropriate for the laboratories they evaluate. The
proficiency test is scheduled independently and not to correspond with the on-site visit. Applicant
laboratories are notified in advance as to the approximate arrival time of the measurement artifact.
Instructions for performing the test, reporting the results, communicating with the reference laboratory, and
shipping are included along with the artifact as part of the proficiency test package. Applicant laboratories
are instructed to perform all required measurements within a reasonable time and are told where to ship the
artifacts once the testing has been completed.

1.7.2.7 Notification of results

NVLAP notifies each laboratory of its own results in a proficiency test. If a laboratory has been evaluated
prior to the completion of the proficiency test, the status of that laboratory’s accreditation is contingent upon
successful completion of proficiency testing. The laboratory's accreditation status may be changed to reflect
a partial accreditation, or may be completely suspended pending demonstration of the laboratory's ability
to successfully complete the proficiency test at a later date.

1.7.3 Traceability
1.7.3.1 Establishing traceability

Laboratories must establish an unbroken chain of comparisons leading to the appropriate international or
national standard, such that the uncertainties of the comparisons support the level of uncertainty that the
laboratory gives to its customers. Generally speaking, the uncertainties of the comparisons increase as they
move from a higher (international or national level) to a lower level standard. This uncertainty chain is the
evidence of traceability and must be documented accordingly. Traceability does not simply mean having
standards calibrated at the national laboratory, but must consider how a measurement, with its corresponding
uncertainty, is transferred from the national level to the calibration laboratory's customers.

1.7.3.2. Considerations in determining traceability

Without measurement assurance, one cannot be reasonably certain that the comparisons have been
transferred properly to the laboratory's customers. The measurement process itself must be verified to be
in control over time. Therefore, traceability is not a static concept that, once established, may be ignored,
but it is dynamic. Process control exercised in each calibration provides the assurance that a valid transfer
of the international or national standard has taken place. This assurance may be accomplished through the
use of tools such as check standards and control charts. Also, the laboratory's primary standards must be
maintained in such a way as to verify their integrity. Examples of this may be having more than one primary
standard to use for intercomparisons, monitoring the primary standard with a check or working standard
(looking for changes), and verifying a primary standard on a well-characterized measurement/calibration
system. Using scientifically sound measurement procedures to transfer the primary standard value to the
working level and the customer's item is essential to establishing traceability. If the procedure itself yields
the wrong result, there is no way the laboratory can perform a calibration traceable to the international or

NIST Handbook 150-2E 8 August 2001


2 Criteria for accreditation
2.1 Introduction

2.11 Applicant laboratories are assessed using the requirements in NIST Handbook 150, NVLAP
Procedures and General Requirements. This guide, NIST Handbook 150-2E, was developed from a NIST
measurement laboratory perspective and provides examples and guidelines, not requirements, to assessors
and interested calibration laboratories on good laboratory practices and recommended standards. Therefore,
the guide language reflects this philosophy through the use of "shoulds" instead of "shalls" (along with other
less prescriptive language) when describing criteria. The requirements presented here are not absolute since
specific requirements depend on the measurement uncertainty for which an applicant laboratory wishes to
be accredited. This is a business decision for each laboratory and beyond the scope of NVLAP. Simply
stated, to be accredited, an applicant laboratory must have a quality system and be able to prove (and
document) that it is capable of doing what it says it does (i.e., correctly calibrate to a stated uncertainty)
within the framework of NIST Handbook 150. Accreditation will be granted, and therefore may be
referenced in calibration reports, etc., only for those specific parameters, ranges and uncertainties using
calibration methods and procedures for which a laboratory has been evaluated. Calibrations performed by
a laboratory using methods and procedures not considered appropriate for the level of measurements being
made, and which have not been evaluated by the accreditation process, are outside the scope of accreditation
and may not be referenced as "accredited" calibrations on calibration reports, etc.

2.1.2 Section 2.2 provides general interpretations of the NIST Handbook 150 criteria for optical radiation
calibrations. Sections 2.3 through 2.9 provide specific calibration guidelines for optical radiation
measurements and references to related standards and documents. This guide is dynamic in that new
parameters may be added and existing criteria updated and improved.
2.2 General criteria for optical radiation calibrations
2.2.1 Scope
2.2.1.1 This section contains the technical criteria in accordance with which a laboratory should
demonstrate that it operates, if it is to be recognized as competent to carry out optical radiation calibrations.
The optical radiation calibrations currently included in the accreditation program are:
a) Radiance temperature

1) Optical pyrometry/radiance temperature
b) Photometric measurements

1) Luminous intensity and illuminance

2) Luminous flux

3) Spectral flux and light source color

4) Luminance

5) Color temperature

NIST Handbook 150-2E 10 August 2001


Contents

Preface . 2... cece cece cence eee e eee e eee een een een eee een tenses beeen eee eeeeee v
Acknowledgments .............+
SUMMATY 0. cece cere e eee eee ee eee ee eee eee e eee een eeeees viii
1 General information ............... Fa
1.1 Purpose.............06-
1.2 Organization of handbook ...........eceee cece eeeeeeeeeeee
1.3 Description of Calibration Laboratories Accreditation Program ............+1
1.4 References 00... . ccc cece cece cece ene e een eee eee een eee eeeenee enna 2
1.5 Definitions .............. bee eeeees 4
1.6 NVLAP documentation .......... 4
1.7 Assessing and evaluating a laboratory eee cece eee ee eee reece eee
2 Criteria for accreditation ©0000... 0... ccc cece cece eee eee eee ene e eee eeeeeneee 10
2.1 Introduction .............+06+ beeen eee eeeeeeeeee ---10
2.2 General criteria for optical radiation calibrations ... -10
2.3 Radiance temperature ......... cc cece cece cece cece eeeeenees -13
2.4 Photometry ............eeeeeeeeeeeee PS
2.5 Spectrophotometry ......... cece e cece eee etter ence tee eesneeee wee 18
2.6 Spectral radiance and spectral irradiance ............
2.7 Spectral responsivity ............eceeeeeeeeeeeees
2.8 Laser power and energy ..
2.9 Optical fiber power ..............56-

iti


2.5.4 Accommodation and environment

2.5.4.1 The temperature and humidity of the laboratory environment should be monitored and declared
in the test report.

2.5.4.2. When ultraviolet sources are used, adequate exhaust and ventilation should be provided. UV eye
protection should be worn by the occupants of the room.

2.5.4.3 Lasers should be shielded from direct eye view of the operator or eye protection rated for the class
of the laser should be worn.

2.5.5 Equipment and reference materials

Equipment for spectrophotometric measurements should be calibrated and carefully documented in
accordance with standard practices. The appropriate spectral sources, reference materials, predispersing
devices, monochromators, integrating/averaging spheres, detectors and/or aperture should be properly
selected and maintained for each specific spectral region.

2.5.6 Calibration methods

Laboratories may use the instrumentation and test procedures described in the reference documents.
Calibration methods should consist of well-documented and established techniques that are reviewed
periodically in order to embody accepted laboratory standard practices.

2.5.7 Handling of calibration items

2.5.7.1 Care should be exercised when handling reference standards; never touch the front surface of the
standard.

2.5.7.2 Extreme caution should be used when it is necessary to clean reference standards. Cleaning the
standards can damage the surface and the measurement history.

2.5.7.3 It is strongly recommended that a face mask be worn to prevent contamination of the calibration
surface. It is further recommended that both hands be covered with lint-free gloves to prevent fingerprints
on calibration surfaces. If a whole glove confines movement, the non-contact portion of the glove may be
removed, or finger cots may be used.

2.5.7.4 If dust must be removed from the test surface, it is recommended that a clean air bulb with low
airflow be used so as not to generate condensation.

2.5.8 Certificates and reports

The calibration report should include the wavelength versus measured parameters, and experimental
parameters specified by the customer.

NIST Handbook 150-2E 19 August 2001


National Institute of Standards and Technology
NIST Handbook 150-2E

34 pages (August 2001) *

CODEN: NIHAE2

U.S. GOVERNMENT PRINTING OFFICE
WASHINGTON: 2001

For sale by the Superintendent of Documents
U.S. Government Printing Office
Washington, DC 20402-9325

NVLAP AND THE NVLAP LOGO

The term NVLAP (represented by the NVLAP logo)
is a federally registered certification mark of the
National Institute of Standards and Technology and
the federal government, who retain exclusive rights
to control the use thereof. Permission to use the term
and/or logo is granted to NVLAP-accredited
laboratories for the limited purposes of announcing
their accredited status, and for use on reports that
describe only testing and calibration within the scope
of accreditation. NIST reserves the right to control
the quality of the use of the term NVLAP and of the
logo itself.


2.9.8 Certificates and reports

2.9.8.1 The report should describe the method and associated instrumentation used to determine the
response of the test detector to a measured amount of radiation input. The measurement description should
include all pertinent information about the test detector conditions (such as power range setting,
connector/fiber types, wavelength setting, etc.).

2.9.8.2 The report should give the average output response of the test detector relative to the power
incident onto the detector at wavelengths and power levels used.

2.9.8.3 The report should give the associated measurement uncertainty for each calibration number
provided for the test detector. The report should describe the pertinent uncertainty components and the
method used to combine these factors into a single uncertainty.

NIST Handbook 150-2E 27 August 2001


2.7.2 References

a) "Spectroradiometric Detector Measurements: Part] - Ultraviolet Detectors and Part II - Visible to Near-
Infrared Detectors," NIST Special Publication 250-41, T.C. Larason, S.S. Bruce, and A.C. Parr (1998).

b) "Spectroradiometric Detector Measurements: Part III - Infrared Detectors,” NIST Special Publication
250-42, A.L. Migdall and G.P. Eppeldauer (1998).

c) "Determination of the Spectral Responsivity of Optical Radiation Detectors," CIE Publication 64.

d) "Optical Radiation Measurements," Editors: F. Grum and C. J. Bartleson, Vol. 1: "Radiometry," F.
Grum and R. J. Becherer; Vol. 4: "Physical Detectors of Optical Radiation," W. Budde. Academic
Press, New York, Vol. 1: Vol. 4: 1983.

e) C.L. Wyatt, "Radiometric Calibration: Theory and Methods," Academic Press, New York, 1978.

f) _E.F. Zalewski and C. R. Duda, "Silicon Photodiode Device with 100 % External Quantum Efficiency,"
Applied Optics 22, 2867-2873 (1983).

g) "New Developments and Applications in Optical Radiometry III," Metrologia 28 (1991).

h) "New Developments and Applications in Optical Radiometry IV," Metrologia 30 (1993).

2.7.3 Statistical process control

The laboratory should have an adequate number of working standard detectors that span the spectral range
of the detectors calibrated by the laboratory. A laboratory performing frequent calibrations should have a

group of at least three working standards.

Control charts are a statistical tool used for tracking a process or performance over time. Working standard
performance should be checked on a periodic basis.

2.7.4 Accommodation and environment

2.7.4.1 In some cases, the temperature and humidity of the laboratory environment should be monitored
and recorded.

2.7.4.2 Appropriate eye protection or shielding should be used if a potentially hazardous source is used
(e.g., uv source or laser). Other safety hazards should be properly handled (e.g., proper ventilation for ozone
producing lamp).

2.7.5 Equipment and reference materials

2.7.5.1 The laboratory should maintain a reference standard detector whose spectral responsivity
calibration is obtained from or traceable to NIST. This reference standard should span the spectral range of
the calibration service provided by the laboratory. The reference standard should be verified annually or on
a well-derived and documented interval.

2.7.5.2. The laboratory should maintain a working standard detector(s) whose spectral responsivity is
traceable to NIST through the laboratory's reference standard detector. The working standard(s) should span

NIST Handbook 150-2E 22 August 2001


1.7.1.4 The assessor, or the assessment team, does the following during a typical on-site assessment:

a) Conducts an entry briefing with the laboratory manager to explain the purpose of the on-site visit and
to discuss the schedule for the day(s). At the discretion of the laboratory manager, other staff may
attend the briefing.

b) Reviews quality system manual, equipment and maintenance records, record-keeping procedures,
laboratory calibration reports, and personnel competency records. At least one laboratory staff member
must be available to answer questions; however, the assessor may wish to review the documents alone.
The assessor(s) d6es not usually ask to take any laboratory documents with him/her, and previously
supplied documents will be returned.

c) Physically examines equipment and facilities, observes the demonstration of selected procedures by
appropriate personnel assigned to perform calibrations, and interviews the personnel. The
demonstrations must include preparation for calibration of devices, and the setup and use of measuring
and test equipment, standards and systems.

d) Holds an exit briefing with the laboratory manager and staff to discuss the assessment findings.
Deficiencies are discussed and resolutions may be mutually agreed upon. Items that must be addressed
before accreditation can be granted are emphasized, and outstanding deficiencies require response to
NVLAP within 30 days. Items that have been corrected during the on-site and any recommendations
are specially noted.

e) Completes an On-site Assessment Report, as part of the exit briefing, summarizing the findings. The
assessor(s) attaches copies of the completed checklists to this report during the exit briefing. The report
is signed by the lead assessor and the laboratory's Authorized Representative to acknowledge the
discussion. This signature does not necessarily indicate agreement; challenge(s) may be made through
NVLAP. A copy is given to the representative for retention. All observations made by the NVLAP
assessor are held in the strictest confidence.

1.7.2 Proficiency testing
1.7.2.1 Background

Once the quality system review and on-site assessment steps have been satisfactorily completed, it is
necessary to gather another set of data points to aid in deciding whether or not the applicant laboratory is
competent to perform calibrations within the fields of interest to the uncertainties claimed. In the eight fields
of calibration covered by Handbooks 150-2A through 150-2H, there are approximately 85 parameters of
interest. Under most parameters there are several subsets, referred to as ranges. For example, in the
Electromagnetic DC/Low Frequency field, the de resistance parameter can range from .001 Q to the
teraohm, TQ (1 x 10) level in decade values. In view of the many possible ranges, proficiency testing could
be conducted in thousands of areas. NVLAP reserves the right to test by sampling in any area; hence,
applicant laboratories must be prepared, with reasonable notice, to demonstrate proficiency in any of a
number of parameters.

1.7.2.2 Proficiency testing vs. measurement assurance
There is an important difference between proficiency testing and measurement assurance. The objective of

proficiency testing is to determine through a measurement process that the laboratory's measurement
compares favorably with the measurement of the audit laboratory (NIST or one designated by NVLAP),

NIST Handbook 150-2E 6 August 2001


national standard. Handling the laboratory's standards affects the measurement process, and therefore the
ability to transfer the standard's value to the customer. Examples of handling problems are dirty or
improperly cleaned standards, maintaining standards in an improper environment, not maintaining custody
and security, and improper handling of standards during the measurement process.

1.7.3.3. Relationship to existing standards

The above discussion illustrates how traceability is dependent on many aspects of the measurement process
and therefore must be considered in all phases of calibration. It is not just coincidental that the factors
addressed above are niain topics of concern in ISO/IEC 17025:1999.

1.7.4 Uncertainty

NVLAP recognizes the methodology for determining uncertainty as described in the Guide to the Expression
of Uncertainty in Measurement, published by ISO. To be NVLAP-accredited, a laboratory must document
the derivation of the uncertainties that it reports to its customers. These uncertainties will appear on the
scope issued to each accredited laboratory to an accuracy appropriate to the standards, procedures, and
measuring devices used.

NIST Handbook 150-2E 9 August 2001